1. Field of the Invention
The present invention relates to a solid state image sensing device used in a television camera, an electronic still camera, and the like and, more particularly, to a solid state image sensing device having an improved discharging function.
2. Description of the Related Art
Solid state image sensing devices have been widely used in television cameras, electronic still cameras, and the like. In an inoperative state of such a solid state image sensing device, charge is stored in the respective components of the device. Upon operation of the device, it takes a long period of time to transfer and discharge the charge a plurality of times through vertical and horizontal registers. More specifically, in the inoperative state of the solid state image sensing device, a large amount of change is stored in photodiodes, the vertical and horizontal registers, and the like. Upon its operation, the charge stored in these components must be discharged first. For this reason, the charge stored in the vertical and horizontal registers is generally transferred through the vertical and horizontal registers in the normal transfer direction and is then discharged. Alternatively, the charge stored in the vertical register is transferred in an opposite direction and is then discharged to a drain at the end of the vertical register. The charge stored in the photodiodes is transferred to the vertical register and discharged therefrom.
Even if the above operation is performed at high speed, the charge must be discharged a plurality of times since a large amount of charge is stored in the above components in the inoperative state. It takes a long period of time from the start to the end of discharged. In particular, in an electronic still camera, the solid state image sensing device is started upon depression of a shutter. If it takes a long period of time to completely discharge the stored charge, a user must wait for a long period of time to take a picture while depressing the shutter. The user may miss a shutter chance. In addition, charge in a photoelectric transducer film is trapped in a trap level present in the film and is discharged after some period of time. Therefore, an after image characteristic in the solid state image sensing device is undesirably degraded. When a bias charge is applied to a light-receiving/storing section in order to reduce an after image, a scratch or fixed pattern noise is generated on an image by variations in charge amounts during discharge.